Balance/unbalance conversion adaptor

PURPOSE:To improve the balance properties of a transmission line of the balanced side for a balance/unbalance conversion adaptor which converts a balanced signal into an unbalanced one. CONSTITUTION:A balance/unbalance converter 5 consists of a transformer containing a toroidal core 51 and a coaxial cable 2 piercing through the center part of the core 51 for transmission of the unbalanced signal. Furthermore a cylindrical shielding part 6 is added to store the core 51 and provided with a shielding plate 61 which secures the shielding between the transformer and the connection part of the balanced side. Then a ground line 54 is provided to the cable 2 which transmits the unbalanced signal, and the line 54 is earthed to the plate 61 at plural points. In such a constitution, the leaked magnetic flux can be reduced and the balance properties of a transmission line can be improved at the balance side.